The Time Course of Preparation after a First Peak: Some Constraints of Reacting Mechanisms

The aim of this work was to study the time-course of preparation when a two choice stimulus arrives, in a predictable (Experiment I) or unpredictable (Experiment II) manner, after the moment at which it was expected. Subjects watched the screen of an oscilloscope on which a spot moved horizontaly. Vertical lines marked (a) the starting point of the spot's course, t0, and (b) the points in time, t1 … t1, at which the stimulus could arrive. In Experiment I five intervals between t1 and t1, ranging from 150 to 900 ms were used in different blocks of trials. In Experiment II three t1-t1 intervals, ranging from 100 to 400 ms mixed in a random way were used. In both cases subjects were asked to react as fast as possible when the stimulus was presented at moment t1. The time course of preparation was studied when the stimulus arrived at moment(s) t1. The results show that reaction time reaches a maximum 250 ms after t1, irrespectively the predictability of the t1-t1 interval. It is also shown that an interval of about 1 s was necessary to obtain reaction times as rapid as those observed at moment t1. The results are discussed in terms of the evolution of an hypothetical “state of preparation” after a maximum which remains unused.